Fuel injection system



June 23, 1936.

A. M. ROTHROCK FUEL INJECTION SYSTEM 2 Sheets-Sheet 1 Filed March 29, 1934 Patented "June 23, 1936 UNITED STATES PATENT OFFICE FUEL INJECTION SYSTEM Addison M. Rothrock. Langley Field, Va.

Application March 29. 1934, Serial No. 718,000

2 Claims.

(Granted under the act of March a, 1883, as

amended April 30, 1928; .370 O. G. 751) V systems for internal combustion engines of spark ignition, hot spot ignition, or compression ignition types, and the difference between the injection system submitted in the pending application above referred to and' the system herein described is in the method of releasingthe pressure from the pressure reservoir and in the methd of controlling the fuelquantity injected. The "original application describes an automatic method of pressure release-in which a spring-tensioned valve opens automatically in response to a predetermined pressure and the cessation of injection is caused by destroying the pressure in the reservoir by mechanically opening a valve. In the system herein disclosed, the pressure release valve is opened mechanically and the cessation of injection is caused, -not by any me-' chanical action of the injection system but by the return of the hydraulic pressure wave transmitted through the injection tube or by the dissipation of this wave in the form of kinetic energy of thedischarging fuel.

With the foregoing in view, the invention consists in the novel arrangement, combination and operation of parts hereinafter described in detail with reference to the accompanying drawings," wherein:

Figure 1 is a longitudinal sectional view of a fuel pump embodying the invention and including a port pressure release valve shown in the discharge position.

' Figure 2 is asectional fragmental view of the pump structure with they port pressure release valve in the suction position. w

Figure 3-is a similar sectional viewof a fuel pump with poppet pressure release valve.

' Figure 4 is a sectional view of a modified pump structure, and 1 Figure 5 is a similar view of a further modified fuel-pump. 1

Figure 6 is a top plan view of the pump plunger used in the modified structure of Figure 5.

The drawings illustrate novel designs of injection fuel pumps incorpofating theprinciple of the invention.

Referring more particularly to Figures 1 and 2, the injection fuel pump therein shown comprises a pump cylinder l and a reservoir 2 separably joined together by bolts and flanges, as indicated at 3. The pumpplunger 4 carries at its lower end a follower block 5 which has a pin 6 supporting a roller I. The roller bears upon an eccentric cam 8 fixed on a cam-shaft 9 in the oil well I0 in the base of the pump. The cam shaft is rotated from any suitable source, such as from ,the engine 'to which the pump is ap-- plied, and the cam 8 rotating with the shaft coacts with the plunger follower in reciprocating the plunger. The plunger is guided in its-movement by the follower, which has sliding contact with the inner wall of the pump cylinder, and also by a plunger bushing, or sleeve ll carried by the reservoir 2, as shown in Figure 1. The plunger bushing is secured in the reservoir by a retaining plug l2 screwed into the threaded extension l3 of the reservoir. A plunger-tensioning spring [4 encircles the plunger between the extension l3 anda spring-seating cap or follower l5 fitting over the enlarged circular base iii of the plunger; the spring and cap serving to maintain contact between the base of the plunger and the plunger follower. The plunger is of such a length that during the reciprocation thereof, its upper end moves inwardly and outwardly of, the reservoir pressure chamber, l1.

Fuel enters-the reservoirchamber through the inlet connection [8 which has a check valve I9 to prevent fuel from being forced back into the inlet line. The reservoir also has a fuel outlet passage 20 to the injection tube 2| and the injection valve 22; the injection tube having ascrew threaded connection with the reservoir as shown at 23. The plunger bushing H has a port 24 which is aligned with the fuel outlet passage 20. A plunger bushing aligning plug is shown at 25. The passage of fuel from the reservoir chamber H to the outlet passage 20 is controlled by the upper or valved end of the i plunger 4 which is recessed inwardly of the extreme upper end. 'to provide a fuel chamber 26. having vertically. spaced ports 21 and 28 adapted to register respectively with the plunger bushing port 24. The passage of fuel from the fuel outlet 20 to the injection tube 2| is controlled by a load-control or restriction valve comprising a cylindrical valve stem 29 operating in a bore in the reservoir body and threadedly engaged in a valve bushing 30 screwed into the upper enlarged end of the valve bore. The valve is rotatedby a handle 3| and when fully closed engages. the valve seat 32 in the fuel outlet passage 20. In the operation of the pump asthe c'am B rotates, the plunger 4is forced into the reservoir compressing the fuel in the reservoir chamber H and building up a high hydraulic pressure (6,000 pounds per square inch for the pump shown). When the port 28 in the plunger uncovers the port 24 in the sleeve II, as shown in Figure 1, the fuel under pressure in the reservoir suddenly expands through the passage 20 connected with the port, transmitting a pressure wave toward the load-control valve 29. When the load-control valve is opened, the wave travels on through the injection tube 2| connected to the injection valve 22. The injection valve, being of the automatic type is openedby the force of the hydraulic pressure wave, and fuel is discharged through the discharge orifice. Discharge continues until the pressure at the injection valve drops below the injection valve closing pressure. When the load-control valve is fully opened, the wave is transmitted to the injection valve in full intensity. When the load-control valve is partly opened (as shown), part of'the wave is reflected back to the reservoir and the rest is transmitted through the injection tube to the injection valve. Because of the partial reflection, the fuel quantity discharged is decreased. When the load-control valve is fully closed, the full wave is reflected back to the reservoir and there is no discharge. The plunger port 21 is uncovered. when the plunger is at the bottom of the stroke and the purpose of this port is to permit the residual pressure in the injection tube following injection to drop to a low value before the succeeding injection.

The operation of the pump illustrated in Figure 3 is in general the same as that of the preceding pump. Insteadof the port release, a poppet valve release operated through a rocker arm is used. In this arrangement, the fuel outlet passage 20a of the reservoir is normally closed by a valve 33 held to its seat by a spring 34 and unseated' by the impact of the upper end of the rocker arm 35. The rocker arm is pivotedat 36 and carries at its lower end a roller 31 hearing against the plunger-operating cam Oil by means of which the rocker arm is actuated. Contact between the cam 8a and the roller 31 is maintained by. the pressure on the upper end of the rocker exerted by the spring assembly 3'. The load control is through the valve 29a and works in the same manner as that through the valve 29 already described. With the poppet valve control, the poppet valve is held open until after the pump plunger returns to or close to the bottom of-its stroke so that the residual pressure in the injection tube is automatically released to the reservoir.

With either pump, the volume of fuel in the injection tube is in general greater than that in the reservoir so that injection must be by the pressure-wave or pressure. impulse principle. In a'pump built for experimental purposes and'mounted on a test engine, the volume of the reservoir is 0.80 cubic inch. ,The volume of the injection tube is 1.37 cubic inches. As has been stated before, the hydraulic pressure in the reservoir caused by the plunger displacement is 6,000 pounds per square inch. Consequently, the

hydraulic pressure in'the whole system caused by W Placement would b only .0-80 m X 5000- ,200 pounds per square inch. The injection-valve opening pressure is set at 4,200. pounds per square inch. Therefore, it can be definitely stated that the discharge is caused by a hydraulic pressure wave resulting from the sudden release of the fuel under pressure in the reservoir to the injection tube.

In the pump structure shown in Figure 4, the reservoir 26 is an integral part of the pump body, being located at the upper end of the pump cylinder lb, and containing the fuel reservoir chamber I lb in which is located the pressure release valve opening and plunger-returning spring Mb. The pump plunger slides in the guide bushing I lb secured in the pump cylinder and at the bottom of the reservoir chamber by the retaining screw plug l2b. The base 16b of the plunger rests on the follower block 5b and is reciprocated by the cam 8b operating against the roller lb of the follower assembly. The spring seating cap or follower l5b-which seats the lower end of the spring I 4b is cupped over the'upper end of the plunger and a retainer plate 39 for the upper end of the spring is centered on the lower shouldered stem portion of the pressure release valve 33b, the head of which engages the valve seat 40 while the stem depends into the reservoir cham- 2n ber i'lb as'illus'trated. ,A valve return spring 34b is confined between the valve head and a retaining plug 4! screwed into the reservoir, as shown. The valve 33b has a slide bearing in a valve bushing 42 secured by a retaining plug 43. Fuel enters the reservoir though the inlet connection lab and the fuel inlet passage 44 which communicates at its inner end with a fuel passage 45, leading to the reservoir chamber "b, and also with a fuel passage 45 to the pressure release valve 33b. The pressure release valve controls the flow of fuel from the passage 44 to the fuel passages 41 and 20b leading from the pressure release valve to the injection tube 2lb. The fuel inlet connection llb has a ball check valve I9b and the fuel passage 20b is grooved at 48 to seat the gate 49 at the lower end ofthe' load control valve stem 29b. The load control valve'slides in a valve bushing 30b above which is a bushing retaining plug 50 seating the lower end of a compression spring 5i confined between the plug and the circular collar 52 of the load control valve stem. The spring is tensioned to exert a thrust upward on the valve stem for holding the valve gate 49 clear of the fuel passage 20b. Means for depressing the valve stem to whollyor partially close the gate valve comprises a hand wheel 3lb on the upper end of screw 53 which is threaded in a support 54 screwed into thereservoir body as shown. The inner end of screw 53 bears on the valve stem, head 55 and 'when fully screwed upon the same forces the pressing spring Nb and displacing fuel in the reservoir chamber l'lb. This displacement of the fuel causes the fuel in the reservoir chamber and in the pasages 44, 45, and 46, to be compressed. The compression of the fuel results in a hydraulic pressure against the retaining walls of thereservoir "b and the passages 44, 45 and 45 and forces the ball check valve l9b against its seat so that fuel will not be forced into the intake connection l8b. The hydraulic pressure of the compressed fuel also acts against the pressure release valve 33b, forcing the same against its seat 40 so that no fuel can be forced into the passages 41 and 20b. As the pump plunger is forced towards the top of its upward stroke, the

' pressure than would be the case if the two pasretainer 39 is also increased. However, the differential hydraulic pressure on the pressure release valve causes the latter to remain tightly seated. This diiferential pressure is caused by the fact that whereas the hydraulic force acting to open the pressure-release valve 33b acts on the cross-sectional area 63 of the end of the valve stem, the hydraulic force acting to close the valve acts on the cross-sectional area 64 of the top of the valve stem. The top area 64 is greater than the bottom area 63 and there is, therefore, a hydraulic force or diiferential pressure causing the valve to remain tightly seated. Before the plunger reaches the end of its stroke, that is, when it is at a height of approximately of the total stroke, the follower l5b engages the lower end 'of the pressure release valve stem and causes the valve. to lift slightly from its seat. As soon as the pressure release valve lifts slightly from its seat, the hydraulic force caused by the compressed fuel is releasedbecause the force new acts equally to both open and close the pressure release valve. The equalization of the hydraulic force onthe injection valve stem is assisted by the volume of fuel in the passage 41 which has a cross sectional area in excess of that of passage 201). This is due to the fact that, inasmuch as the area of the passage 41 is greater than the area of the passage 2%, there is a build-up of pressure in the passage 41. This build-up of pressure tends to equalize the hydraulic forces tending to open and tending to close the pressure-release valve. To express it in another way, the decrease in cross sectional area as the fuel passes from passage 41 to. passage 2% results in a lower velocity in the passage '41 with a consequently greater static sages had the same area. As a'result of this release of the hydraulicforce, the spring i4b causes the pressure valve 3312 (through the retainer 39) to lift with extreme rapidity. This sudden lift of the pressure release valve allows the fuel which has been compressed in the reservoir chamber 111) and the passages 44, 45 and 46 to suddenly expand against the fuel atja lower pressure in the. passage 41. This sudden expansion of the compressed fuel into the passage 41 causes a hydraulic pressure wave of high in- .tensity to be transmitted through the passage 20b and the injection tube 2m and thence to the injection valve. This hydraulic pressure wave travelling with the velocity of sound in the 'medium causes the fuel to beinjected from the injection valve at a high velocity. The cessation vof the pressure wave is caused'by the release of the hydraulic force caused by the expansion of the compressed fuel in the reservoir I1?) and the pasages '44, 45 and 46;. As a result, although the hydraulic pressure wave is intense in mag- .nitude, the wave is short in duration. The hyjust been described is so rapid that it is completed before plunger 41 reaches the top of its stroke. The remaining portion of the stroke of the plunger results in some further pressure increases, but does not cause further injection of fuel because the hydraulic pressure throughout the injection system is now too low to result in any further injection through the injection valve. As the plunger 4b starts on its down stroke the liquid fuel is still further decompressed until a pressure is reached which is lower than that of the incoming fuel at the inlet connection -l8b. As a result, the check valve I9!) is forced open and fuel flows into the passage 44 and so to passages 45, 46,41, and 20b, as well as the injection tube 2| b and injection valve, and the reservoir I 1b. As the plunger approaches the 'bottom of its stroke, the spring 3412 exerts a greater force on the pressurerelease valve 331) than does the spring l1b. Consequently the pressure release valve is forced against its seat 40 and the cycle is then repeated for the succeeding injection. The amount of fuel discharged is controlled by the gate valve 291). When the gate valve is fully opened, the fuel intensity of the pressure wave is. transmitted to the injection tube and so to the injection valve. Any partial closing of the valve causes part of the pressure wave to be reflected back to the reservoir chamber Nb and the remainder continues to be transmitted through the injection tube and thence to the injection valve. Because of the decreased intensity of the pressure wave the fuel quantity discharged is decreased. When the gate valve is fully closed, all of the pressure wave is reflected back to thereservoir chamber and no fuel is injected.

The general principle of operation of .the injection system illustrated in Figure 5 is the same as that shown in Figure 4. The difierence between the systems embodied in Figures 1 to 4 inclusive and .the system shown in Figure 5 is in the fuel inletto the system and in the method of quantity of fuel injected is controlled by limiting the amount of liquid fuel compressed in a reservoir and so limiting the intensity of a hydraulic pressure wave caused by fuel in a reservoir at a higher pressure suddenly expanding against U liquid fuel in a tube at a lower pressure. In the pump structure shown in Figure 5, the pump plunger 40 is at the bottom of its stroke so" thatthe top of the plunger uncovers the fuel inlet passage 56. As the plunger starts up, the inlet port is covered and the fuel is compressed in the reservoir I10 and 450 and the passages 51, 58 and 59, the latter leading from the reservoir to the pressure release valve 33c. The initial opening of the pressure release valve is caused by the engagement of the valve-opening spring follower I with the valve stem follower 39c and the subsequent rapid opening of the pressure release valve 330 is caused by the force of the valve opening spring [40 which has been compressed by the upward motion of the pump plunger, the action being similar to that described for Figure 4. The quantity of fuel injected is controlled by rotating the plunger carried load control sleeve 60 by means of the rack 59. Rotating the sleeve in turn rotates the plunger lc which is provided with a load control slot or groove 52. When the .valve. .In the system shown in Figure 5, the

plunger is rotated, the groove comes in line with the inlet passage 56. As a result, the position of groove 62 with reference to the passage 56 determines that part of the stroke of the pump plunger during which fuel is forced back through the inlet passage 56. The amount of fuel forced back through the passage 56 determines the amount of fuel compressed in the reservoir I10 and 45c and in the passages 51, 58, and 59. The amount of fuel compressed in the reservoirs He and 45c and in the passages 51, 58 and 59 determines the hydraulic pressure in the reservoir I10 and 450 and in the passages 51, 58 and 59 at the time the plunger 40 causes the follower l5c to engage the follower 39c and as a result determines the hydraulic pressure when the pressure release valve lifts from its seat 400. The magnitude of this hydraulic pressure determines the intensity of the hydraulic pressure wave which travels through the passages 41c and 200 and through the injection tube Zlc connected to the passage 20c and to the injection valve connected with the.

injection tube. The magnitude of this hydraulic pressure wave determines the quantity of fuel injected. This injection system differs from other injection systems in that all the energy for the injection of the fuel is stored in a reservoir and then suddenly released in such a manner that the rate 'offuel injection is independent of the rate of plunger motion and consequently independent of the speed at which the camshaft turns. Furthermore, the injection is controlled entirely by the sudden expansion of a volume of compressed fuel so that although the start of injection is timed mechanically the continuation of the injection is controlled entirely by the hydraulic expansion of the liquid fuel and is, therefore, independent of any mechanical process taking place within the injection system after injection has once started. Injection is completed by the return of the pressure wave which has been transmitted through the injection tube to the injection valve. When the Wave strikes the discharge orifice, part of the energy is consumed as kinetic energy of the dis charging fuel. The remainder of the energy is transformed into potential energy of compression. This potential energy is promptly retransformed into kinetic energy in the form of a pressure wave which is now transmitted back through the injection tube to the reservoir of the pump. The cessation of discharge is caused by the relationships between these energy quantities and by the period of vibration of the oil column in the injection tube. This period is equal to in which 1 is the length of the injection tube, 12 the density of the fuel, E the compressibility of the fuel, and g the gravitational constant. The total amount of energy available for injection is the total amount of potential energy contained in the compressed fuel in the reservoir at the time that the pressure-release valve starts to open. Therefore the cessation of injection is caused by the expansion of this compressed fuel into the injection tube; that is, the cessation is caused by the transformation of the potential energy of the compressed fuel in the reservoir to the kinetic energy of moving fuel in the injection tube and by the decrease in the magnitude of this pressure wave as the transformation becomes complete.

In addition, because the injection of the fuel is caused by a hydraulic pressure wave, only that rapidity.

part of the fuel in the reservoir and its immediate connecting passages is compressed, while any fuel which is in the injection tube and the injection valve is not compressed except for the action of the hydraulic .pressure wave'during the actual 5 injection process. Hence, the displacement of the pump plunger need not be sufficient to compress all the liquid fuel, including that in the injection tube and in the injection valve, but only that liquid in the reservoir and its immediate connectl0 ing passages. Furthermore, the cessation of injection is not transmitted to the inlet line in any way and consequently the inlet line of the system doesnot require any means for damping or destroying a high intensity pressure impulse. In 15 addition, the rate of plunger displacement can be comparatively low so that there are no excessive ,strains imposed on the camshaft as a result of I claim: 25

1. In an injection system, a fuel injection pump having a high pressure reservoir provided with a fuel inlet port and a fuel outlet passage, a plunger movable into said reservoir for compressing the fuel therein, a pressure-release valve normally closing the fuel outlet passage of the reservoir and adapted to be forced against its seat by the hydraulicpressure of the compressed fuel in said reservoir, said valve having a depending portion extending into the pressure reservoir and adapted 35 to be engaged by the plunger before the latter reaches the end of the compression stroke and thereby lifted to slightly unseat the valve for equalizing the hydraulic pressure on the valve, and a valve-lifting spring confined between the 40 said plunger and the depending portion of the said valve to be compressed by the compression movement of the plunger and acting upon the equalization of the hydraulic pressure on the valve by the initial opening of the same, to lift 45 the said valve rapidly to permit the compressed fuelof the reservoir to expand suddenly into the fuel outlet passage.

2. A fuel injection pump provided with a liquid fuel chamber having a fuel-inlet and a fuel out- 50 let, a plunger for producing hydraulic pressure in the fuel chamber, a valve normally closing the fuel outlet and having its head and stem presented to and oppositely acted on by the hydraulic pressure in the fuel chamber whereby the 55 resultant of the differential pressures on the valve acts to seat the latter, said valve being also arranged with its stem disposed in the path of the plunger to be engaged thereby andlifted on the compression stroke of the plunger for unseating the valve at a predetermined point in the said stroke of the plunger, a valve-retum spring pressing against the head of the valve to return the latter to its seat when the said plunger is sub stantially at the bottom of its intake stroke, and a valve-opening spring between the pump plunger and the stem'of the valve to be compressed by the plunger on the compression stroke of the latter, said valve-opening spring reacting when 70 released from its compressed condition by the opening of the valve to lift the valve with extreme ADDISON M. RO'I'HROCK. 

